Hearing devices are wearable hearing apparatuses which are used to assist the hard-of-hearing. In order to accommodate numerous individual requirements, various types of hearing devices are available such as behind-the-ear (BTE) hearing devices, hearing device with external receiver (RIC: receiver in the canal) and in-the-ear (ITE) hearing devices, for example also concha hearing devices or completely-in-the-canal (ITE, CIC) hearing devices. The hearing devices listed as examples are worn on the outer ear or in the auditory canal. Bone conduction hearing aids, implantable or vibrotactile hearing aids are also available on the market. The damaged hearing is thus stimulated either mechanically or electrically.
The key components of hearing devices are principally an input converter, an amplifier and an output converter. The input converter is normally a receiving transducer e.g. a microphone and/or an electromagnetic receiver, e.g. an induction coil. The output converter is most frequently realized as an electroacoustic converter e.g. a miniature loudspeaker, or as an electromechanical converter e.g. a bone conduction hearing aid. The amplifier is usually integrated into a signal processing unit. This basic configuration is illustrated in FIG. 1 using the example of a behind-the-ear hearing device. One or a plurality of microphones 2 for recording ambient sound are built into a hearing device housing 1 to be worn behind the ear. A signal processing unit 3 which is also integrated into the hearing device housing 1 processes and amplifies the microphone signals. The output signal for the signal processing unit 3 is transmitted to a loudspeaker or receiver 4, which outputs an acoustic signal. Sound is transmitted through a sound tube, which is affixed in the auditory canal by means of an otoplastic, to the device wearer's eardrum. Power for the hearing device and in particular for the signal processing unit 3 is supplied by means of a battery 5 which is also integrated in the hearing device housing 1.
Once a technology based on lithium is to be used in a hearing device as an energy source, the cell voltage which is high in comparison with alkali-manganese batteries or zinc-air batteries for instance is to be reduced, if further use is to be made of the technology designed for 1.5 volts. This technology, which is as a rule currently used, is designed for voltages below 1.5 volts for energy saving reasons. Lithium batteries nevertheless provide 3.0 volts and lithium rechargeable batteries even provide a nominal 3.6 volts up to a maximum 4.2 volts.
One efficient method of decreasing the cell voltage to the desired operating voltage, without as a result losing large quantities of energy, consists in the use of a switching controller. Modern hearing systems are in many cases also equipped with radio systems, in order to transmit data wirelessly. One combination of these two technologies now leads to the problem that electromagnetic losses in the switching controller result in interferences in the radio system. In particular, interferences in the range of the fundamental frequency and all multiples of the signal of the switching controller ensue.
Lithium energy sources were previously hardly used for hearing apparatuses. The problem of interferences in a radio system as a result of the switching controller thus practically never occurred in hearing apparatuses. As a result of the demand for rechargeable batteries, more and more lithium systems will however be used in the future.
With hearing apparatuses and in particular with hearing devices, there is generally the desire to reduce the installation size. To this end, the quest to provide as many functions in a hearing apparatus as possible and/or to want to use an energy source which allows for an increased energy transfer, is counterproductive here.